1. Technical Field
The present disclosure relates generally to a susceptor support system used in a semiconductor processing chamber.
2. Description of the Related Art
One of the more common silicon manufacturing processes is a chemical process known as CVD, or chemical vapor deposition. By the chemical vapor deposition process, thin layers of chemical material such as silicon and silicon compounds are deposited upon a wafer by exposing the wafer to the vaporized chemical at high temperature in a reactor chamber. This process generally produces high purity and high performance solid materials.
A chemical vapor deposition generally takes place in a reaction chamber. There are many reaction chamber designs and configurations, each with a different method for performing the fundamental operations, which are: dispensing gases, controlling temperature, and removing byproducts. Gases dispensed into the chamber react not only with materials on a surface of the wafer, but also with walls of the heated chamber wall. This later reactions tend to produce contaminants, which can affect the purity of the chemical deposition on the wafer. To reduce such contaminants, the heat must be localized to the wafer while keeping the walls cool. For example, in U.S. Pat. No. 4,496,609 to McNeilly et al. discloses the use of high intensity lamps and radiant energy to heat the wafer instead of using radio frequency energy.
In the reaction chambers that use radiant energy, the wafer of interest is generally placed on a susceptor which is supported by a susceptor support (also commonly known as a “spider”). FIG. 1 is a simplified view of a chemical vapor deposition machine 100 having a reaction chamber 102. In the reaction chamber 102, a wafer 104 is subjected to a deposition process. Through a chemical reaction between gas applied to the chamber 102 and the material on the wafer 104, an additional layer is formed on the wafer 104.
This chemical reaction also requires the application of heat, which is provided to the wafer 104 through a susceptor 6. The susceptor 6 is supported by a susceptor support 8. The susceptor support 8 is configured to be received by a rotatable shaft 10 that is coupled to a motor 112.
The chemical vapor deposition machine receives a cassette 114 carrying a plurality of wafers 104. The plurality of wafers is transported from other machines in the wafer formation process. A robotic arm 116 grabs the wafer 104 from the cassette 114 and transports the wafer into the reaction chamber 102. A plurality of pipes 117 provide the reaction gases into the chamber and also create vacuum conditions by removing ambient air from the chamber 102.
Once positioned on the susceptor, the wafer is heated and a layer or layers of material are chemically deposited thereon. Not shown in the figure are heating elements and a thermocouple. The thermocouple fits a hollow area or interior cavity inside the rotatable shaft. The thermocouple is coupled to the motor to detect temperature changes during the deposition process.
As reactant gas enters the heated chamber, chemical deposition process starts on the wafer 10 as the gas reacts with the material already on the wafer. The thermocouple monitors the temperature of the region under the susceptor, and as necessary to provide uniform heating to the wafer. The susceptor support, being in contact with the susceptor, would then also rotate the susceptor. Even heating of the wafer ensures uniform deposition, less contamination, and less warping of the wafer.
The susceptor 6 may be made of graphite or other opaque material suitable to allow even heating of the wafer placed upon it. As the chamber is heated to high temperature, the susceptor 6 uniformly transfers the heat by to the wafer 104. To ensure even deposition of chemical across the wafer surface, an even temperature across this surface has to be controlled.
On occasions, the wafer may therefore be rotated, and such rotation is generally accomplished through the rotation of the susceptor 6 by the susceptor support 8. The susceptor support engages the susceptor itself through rotationally and horizontally applied forces through ends in direct contact with the susceptor. The susceptor support 8 is capable of turning the susceptor 6 along a central axis as the susceptor support 8 itself is rotated by the shaft 10 on which it sits. This shaft 10, in turn, is rotated by the motor 112 that is part of the reaction chamber 102 itself. In general, the susceptor support 8, and thus the susceptor 6 itself, is rotated throughout the process, and in some embodiments, may be rotated up to 35 revolutions per minute.
A variety of susceptors 6 are used in the industry. The susceptors, typically made of graphite, have various sizes and features that impact how they are supported in the reaction chamber. Some susceptors have a plurality of indentations formed in a back surface of the susceptor. The indentations are formed to receive cylindrical ends of the susceptor supports. In order to align and adequately support the susceptor, the cylindrical ends must be perfectly aligned in the indentations.
Other susceptors have a smooth back surface that is configured to be supported by a susceptor support having a continuous circular ring of quartz that makes contact with the back surface. Over time the susceptor supports are damaged by the processes in the reaction chamber 102. Because of the adverse conditions in the reaction chamber 102, many susceptor supports are made of quartz. Quartz is particularly resistant to degradation caused by heat and by chemicals, like hydrochloric acid, in the reaction chamber. However, repeated exposure does structurally impact the quartz. Forming the circular ring of quartz is expensive and complicated because the quartz is somewhat fragile.
Accordingly, the cylindrical ends described above will weaken and change shape during the processes in the reaction chamber. The change in shape can cause the susceptor to wobble or otherwise become unstable. The instability negatively impacts the uniformity of the layer formed on the wafer 104. Also, the susceptor supports formed as a circular ring of quartz are degraded during these processes. The quartz may degrade unevenly and cause the susceptor to be unstable.
FIG. 2 is an example of a known tip 101 formed on an arm 118 of the susceptor support 8. The tip 101 is a cube such that all sides of the tip are squares. The tip 101 has a flat contact surface configured to fit into a recess on a back surface of the susceptor 8. After several wafer runs, edges of the tip 101 deform and form curves surfaces that cause the susceptor 8 to wobble or slip as the susceptor support tries to turn the susceptor.
Other problems occur with the quartz in the reaction chamber 102. For example, where the shaft 10 couples to the susceptor support 8. Some designs have a tapered end on the shaft that is forced into an opening in the susceptor support 8. The susceptor support 8 is positioned on the tapered end of the shaft 10 and then knocked into place, forcing the shaft and the susceptor support together. This procedure is prone to breakage. Also, with time in the reaction chamber the two surfaces forced together begin to slip. When this slipping occurs, the shaft 10 no longer turns the susceptor support reliably and therefore does not adequately turn the susceptor.
Efforts have been made to mitigate this rotational slippage. In U.S. Pat. No. 7,169,234 to Weeks et al. shaft having a flat surface in the tapered end is provided. The flat surface works with a retaining member formed on the susceptor support and an independent retaining member to positively secure the susceptor support to the shaft. The independent retaining member is fragile, difficult to manufacture, and easily misplaced. Also, this independent retaining member is affected by the hydrochloric gas in the deposition chamber, which weakens this small part. Once weakened, this independent retaining member can break or otherwise fail to keep the susceptor and the shaft from slipping.